rec: cleanup dnstap regression test a bit and try to avoid LeakSanitizer internal...

rec: cleanup dnstap regression test a bit and try to avoid LeakSanitizer internal issue

The issue is that if the test ends *too* quick LeakSanatizer did
not init all thread local data structures yet, and it reports this
and exits with a non-zero exit code:

  Tracer caught signal 11: addr=0x7fc0f2bc0000 pc=0x55bc6eccaeda sp=0x7fc0f29e1d40
  ==10208==LeakSanitizer has encountered a fatal error.
  ==10208==HINT: For debugging, try setting environment variable LSAN_OPTIONS=verbosity=1:log_threads=1
  ==10208==HINT: LeakSanitizer does not work under ptrace (strace, gdb, etc)